1. Field of the Invention
The present invention relates to a process for producing a continuously cast bar of aluminum which has a helical groove and is substantially free from defects on the inner and outer surfaces thereof.
2. Description of the Prior Art
For obtaining a long aluminum bar having a helical groove, there are already known, for example, a method which comprises first preparing a thick bar by casting or the like, working it into a rectilineal bar or a bar having grooves by means of an extruder, etc. and then giving a twist to the bar at its both ends, and a method which comprises grooving a helix continuously on the surface of a bar by means of rolling or the like.
There is also known a method which comprises using a mold having a helically cut groove which constitutes a part of the present invention, and producing a continuous bar having a helical groove, while conducting rotation and withdrawing in conformity with the slope of the helix (U.S. Pat. No. 4,168,738).
Although it is also possible by these conventional methods to obtain a long bar having a continuous helical groove by supplying a raw material bar continuously during the extrusion, it is difficult to avoid staining at the joint surface due to lubricant used in the extrusion or to avoid structural change, etc.
Although it is also possible to bond the respective end faces by welding or the like after completion of an extrusion, the inspection and the detection of defects, if any, at the bond portion require much time and trouble, and further the deformation of the helical groove at the bond portion necessitates complicated and difficult work for readjusting it.
Also when a heretofore known casting into a helical shape is employed, the resulting continuously cast bar of aluminum has defects such as shrinkage cavity inside the bar unavoidably, and has a lot of depressions and protuberances of its surface. Thus, such defects of the inside and surface of the cast pro duct have been unavoidable.